The present invention involves flotation of platinum group metal ore materials during mineral processing operations.
Platinum group metals (PGMs) include platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and Osmium (Os). The PGMs are chemically similar and have common useful properties, such as for example high conductivity, high resistance to corrosion and high catalytic activity. Significant quantities of PGMs are produced from magmatic ore deposits, and particularly basic magmatic ore deposits that are rich in iron and magnesium. Large quantities of PGMs are mined in South Africa and Russia, with smaller quantities being mined in other countries, such as Canada and the United States. Significant primary PGM mining operations are located in South Africa, with smaller PGM primary mining operations in the United States and Canada. By PGM primary mining operation, it is meant that PGMs represent the primary metal value in the ores that are mined. Significant PGM by-product mining operations are located in Russia and Canada, and particularly the Norilsk property in Russia, where large quantities of PGMs are produced as by-products from nickel/copper ores.
PGMs in PGM magmatic ore deposits can occur in sulfide and non-sulfide minerals. Examples of platinum group metal sulfide minerals include braggite ((Pt, Pd, Ni)S), Cooperite (PtS), vysotskite (PdS), laurite ((Ru, Os, Ir)S2) and malanite ((Pt, Rh, Ir)2CuS4). Examples of PGM non-sulfide minerals include sperrylite (Pt4As2), moncheite (PtTe2), platinum-iron alloys (e.g., PtFe, Pt3Fe), various platinum and/or palladium bismuthinides, bismuth-tellurides, and sulfarsenides, rustenburgite (Pt3Sn), isomertierite (Pd11Sb2As2), arsenopalladinite ((Pd8(As,Sb)3), plumbopalladinite (Pd3Pb2), potarite (PdHg) and geversite (PtSb2). In addition to discrete platinum group metal minerals, PGM values are also found in association with base metal sulfides, such as for example as inclusions in or attachments to a base metal sulfide or in solid solution in a base metal sulfide. Examples of base metal sulfides with which PGM values can be associated include nickel-containing sulfides, such as pentlandite ((Fe,Ni)9S8) and/or millerite (NiS), and to a lesser degree copper-containing sulfides, such as chalcopyrite (CuFeS2). PGM metal values can also be associated with other sulfides, such as pyrrhotite. When PGMs are produced as a by-product it is often with nickel operations.
Typical mineral processing operations for PGM ores involve comminution followed by concentration of the PGMs by flotation. The PGM concentrate is then often processed by smelting and refining to produce purified PGM products. Flotation is a critical operation in PGM mineral processing operations, because a high quality concentrate is required for smelting operations and there is significant potential for loss of valuable PGMs to flotation tails during the preparation of such high quality concentrates. One significant complicating factor is that the basic magmatic PGM ore deposits frequently contain significant quantities of sheet silicate minerals, commonly talc (3MgO.4SiO2.H2O) or other talcose minerals. Because of a sheet-like geometry, talc and other sheet silicate minerals have a high natural tendency to float during flotation operations, and the presence of such minerals during flotation complicates preparation of high quality PGM concentrates. A common technique for addressing the high natural floatability of talc is to add an organic chemical depressant, such as for example carboxymethylcellulose (CMC). Large additions of CMC can be required to sufficiently depress talc, and such large additions of CMC can significantly complicate maintenance of desirable froth characteristics and the effectiveness of collectors. This can lead to the use of a complex flotation reagent scheme involving large quantities of reagents, and can result in a flotation operation that is not very robust, in that flotation performance can vary significantly with relatively modest changes in ore feed mineralogy and other characteristics of the feed slurry. The flotation operation can be susceptible to significant losses of PGMs to the tails and must be carefully monitored and controlled to minimize such losses. Also, the use of large quantities of reagents involves significant operational expense in reagent costs. Furthermore, with the use of such large additions of reagents, there can be a significant build-up of reagents in recycled process water which can further complicate processing.
There is a need for improved flotation processing to prepare high quality PGM flotation concentrates, and especially for processing PGM ores from basic magmatic ore deposits.
It is an object of the present invention to address problems noted above with respect to flotation of platinum group metal ore materials, such as for example a platinum group metal primary ore or by-product ore. The present invention provides a method involving flotation of platinum group metal ore materials in which a lead-containing activator reagent, and preferably also a xanthate collector reagent, are added to the platinum group metal ore material prior to and/or during flotation and the flotation is conducted using an oxygen-deficient flotation gas, such as nitrogen gas. With the present invention, flotation of platinum group metal ore materials, and especially those ore materials from basic magmatic ore deposits containing significant quantities of talc or other sheet silicate minerals, can be processed with enhanced recovery of platinum group metal in the flotation concentrate while at the same time promoting a more robust flotation operation that also often has lower reagent consumption. In particular, the flotation of the present invention can typically be performed without the addition of dithiophosphate collector reagents, while achieving a high recovery of platinum group metal in a high quality concentrate. Additionally, in one important embodiment, a depressant reagent is added prior to and/or during flotation to inhibit floating of sheet silicate minerals such as talc. The depressant reagent can often be employed without significant complication of the reagent scheme and without rendering flotation performance overly sensitive to variations in feed mineralogy and other feed slurry characteristics.
The ore material processed with the method of the present invention will include a quantity of platinum group metal with sufficient value to permit commercial mining and processing to recover platinum group metal. In the case of a platinum group metal primary ore, platinum group metal content in the platinum group metal ore material feed to flotation is often at least 1 gram per metric ton of ore, and often at least 5 grams per metric ton of ore, or even at least 10 grams or more per metric ton of ore. In the case of a platinum group metal by-product ore, the platinum group metal content in the ore material feed to flotation can be very low, because the predominant metal value in the ore will be base metal components such as copper and/or nickel. In the case of a platinum group metal primary ore material, the concentrate will typically contain platinum group metal of at least 5 grams per metric ton, more often at least 10 grams per metric ton and often at least 20 grams per metric ton or even 30 grams or more per metric ton. In the case of high grade platinum group metal primary ores, the platinum group metal content of the concentrate can be in excess, and sometimes significantly in excess, of 100 grams per ton of concentrate.
In one embodiment, the ore material includes, in addition to the platinum group metal, a recoverable quantity of one or both of nickel and copper that is concentrated in the concentrate along with platinum group metal during the flotation. In the case of processing a platinum group metal by-product ore, the platinum group metal concentrate will still typically comprise at least 0.5 weight percent and often at least 1 weight percent or even at least 2 weight percent or more of nickel and/or copper. In the case of a platinum group metal by-product ore, the concentrate will often comprise at least 5 weight percent, and typically at least 10 weight percent or even more of copper and/or nickel. In one particular application, the ore material contains significant pentlandite, millerite and/or chalcopyrite content in the flotation concentrate along with the platinum group metal.
In addition to the reagent and flotation gas combination used with the present invention, a significant difference of the present invention with respect to conventional flotation processing of platinum group metal ores is that with the present invention the flotation should be conducted at an acidic pH, preferably in a range of pH 3 to pH 6. Therefore, with the present invention, acid is typically added to the ore slurry prior to flotation to reduce the pH to the desired acidic range. This is a significant aspect of the present invention, because the natural pH exhibited by basic magmatic platinum group metal ores is basic, and conventional processing is to float these ores at a basic pH.
In one preferred embodiment for implementing the method of the present invention, the platinum group metal ore material is subjected to conditioning prior to flotation, to adjust pH of the slurry (typically to lower the pH to a desired acidic pH), to add the lead-containing activator and/or to add the collector reagent. Such conditioning can be performed in a single step or in a sequence of multiple steps. One possible enhancement for the conditioning is to bubble an oxygen-deficient flotation gas, such as nitrogen gas, through the slurry during one or more step during the conditioning. Another possible enhancement for the conditioning is to add a sheet silicant depressant reagent to the slurry. Another possible enhancement is to add a reducing agent to the slurry during the conditioning to reduce the slurry Eh. Any one or more of these enhancements can be implemented alone or any combination with other of the enhancements. In one embodiment involving multiple sequential conditioning steps, the pH of the slurry is first adjusted to the desired acidic pH. Following pH adjustment, then the lead-containing activator reagent is added to the slurry, followed by separate addition of the collector reagent, preferably a xanthate collector reagent. In one possible enhancement to sequential conditioning, a sheet silicate depressant reagent can be added in a separate conditioning step following addition of the collector reagent. In another possible enhancement to sequential conditioning, an oxygen-deficient process gas, such as nitrogen gas, is bubbled through the slurry during one or more, and preferably all, of the multiple, sequential conditioning steps. In one embodiment, the conditioning includes addition of the lead-containing activator reagent prior to or during comminution of the platinum group metal ore material.
For enhanced performance, the Eh of the slurry during flotation should preferably be maintained at a low level to promote effective interaction between particles of the ore material, the lead-containing activator and the collector. In a preferred embodiment the Eh of the slurry immediately prior to and during flotation should be no higher than xe2x88x9250 mV, more preferably no higher than xe2x88x92100 mV, even more preferably no higher than xe2x88x92150 mV and still more preferably no higher than xe2x88x92200 mV (as measured against a platinum electrode relative to a silver/silver chloride reference). Often, an appropriately low Eh is achieved with the addition of acid to lower slurry pH. If further Eh reduction is desired, a reducing agent can be added to the slurry.